Ashless nitrogen and ester containing lubricating oil dispersants have been widely used by the industry. Typically, these dispersants are prepared from a long chain hydrocarbon polymer by reacting the polymer with maleic anhydride to form the corresponding polymer which is substituted with succinic anhydride groups. Polyisobutylene has been widely used as the polymer of choice, chiefly because it is readily available by cationic polymerization from butene streams (e.g., using AlCl.sub.3 catalysts). Such polyisobutylenes generally contain residual unsaturation in amounts of about one ethylenic double bond per polymer chain, positioned along the chain.
The polyisobutylene polymers (PIB) employed in most conventional dispersants are based on a hydrocarbon chain of a number average molecular weight (M.sub.n) of from about 900 to about 2500. PIB having a M.sub.n of less than about 300 gives rather poor performance results when employed in dispersants because the molecular weight is insufficient to keep the dispersant molecule fully solubilized in lubricating oils. On the other hand, high molecular weight PIB (M.sub.n &gt;3000) becomes so viscous that conventional industrial practices are incapable of handling this product in many operations. This problem becomes much more severe as the PIB molecular weight increases to 5000 or 10,000.
Increased amounts of terminal ethylenic unsaturation in polyisobutylene (so-called "reactive polyisobutylene") has been achieved by BF.sub.3 catalyzed polymerization of isobutylene. Exemplary of references disclosing these polymers is U.S. Pat. No. 4,152,499. However, such reactive polyisobutylene materials can still contain substantial amounts of unsaturation elsewhere along the chain. Further, it is difficult to produce such reactive polyisobutylene polymers at molecular weights of greater than about 2,000, and, even so, the reactive polyisobutylenes themselves still suffer the above-noted viscosity increase disadvantages as molecular weights are increased.
Other polymers, such as ethylene-propylene co-polymers and terpolymers containing non-conjugated dienes, have been disclosed as suitable polymers for the preparation of ashless nitrogen and ester dispersants.
U.S. Pat. No. 4,234,435, for example, discloses dispersants prepared from polyalkenes, M.sub.n of 1,300 to about 5,000. The polyalkene can comprise homopolymers or interpolymers of C.sub.2 to C.sub.16 terminal olefins, of which ethylene-propylene copolymers are said to be examples, with specific reference to a copolymer of 80% ethylene and 20% propylene.
However, ethylene-alpha-olefin copolymers of the above molecular weights could be produced using Ziegler-Natta catalysts only in combination with H.sub.2 as molecular weight control in order to terminate the growing copolymer chains within this molecular weight range. Without use of H.sub.2 or other conventional, so-called "chain stoppers", the copolymers produced with Ziegler-Natta catalysts would tend to have molecular weights greatly in excess of the above range. (Such higher copolymers, for example, are widely employed in ungrafted form as viscosity index improvers, and when grafted with nitrogen-containing groups, as described below, are conventionally employed as dispersant-viscosity index improver polymers.) The use of H.sub.2 as a chain stopper has the disadvantage of causing the saturation of the olefinic double bond content of the copolymer. Thus, while lower molecular weight copolymers were theoretically possible to prepare, their low unsaturation content (and the accompanying low graft copolymer yields) would have made their further functionalization by a thermal "ene" reaction, e.g., with dicarboxylic acid moieties in preparing dispersants, highly unattractive.
High molecular weight ethylene-propylene polymers and ethylene-propylene-diene terpolymers, having viscosity average molecular weights of from about 20,000 to 300,000, are generally produced employing Ziegler catalysts, generally VCl.sub.4 or VOCl.sub.3 with a halide source, such as organoaluminum halides and/or hydrogen halides. Such high molecular weight EP and EPDM polymers find use as viscosity index improvers. See, e.g., U.S. Pat. Nos. 3,563,964; 3,697,429; 4,306,041; 4,540,753; 4,575,574; and 4,666,619.
The concept of derivatizing V.I. improving high molecular weight ethylene copolymers, with acid moieties such as maleic anhydride, followed by reaction with an amine, to form a V.I.-dispersant oil additive is known in the art as indicated by the following patents.
U.S. Pat. No. 3,316,177 teaches ethylene copolymers of at least. 50,000, such as ethylene-propylene, or ethylene-propylene-diene, which are heated to elevated temperatures in the presence of oxygen so as to oxidize the polymer and cause its reaction with maleic anhydride which is present during the oxidation. The resulting polymer can then be reacted with alkylene polyamines.
U.S. Pat. No. 3,326,804 teaches reacting ethylene copolymers with oxygen or ozone, to form a hydroperoxidized polymer, which is grafted with maleic anhydride followed by reaction with polyalkylene polyamines. Preferred are ethylene-propylene copolymers, having M.sub.v from 100,000 to 500,000, prepared by Ziegler type catalysts.
U.S. Pat. No. 4,160,739 teaches an ethylene copolymer (M.sub.v =10,000 to 200,000) which is grafted, using a free radical technique, with alternating maleic anhydride and a second polymerizable monomer such as methacrylic acid, which materials are reacted with an amine having a single primary, or a single secondary, amine group.
U.S. Pat. No. 4,161,452 relates to graft copolymers wherein the backbone polymer is a polymeric hydrocarbon such as EP copolymer or EPDM (M.sub.v =10,000 to 200,000) and the grafted units are the residues of an addition copolymerizable monomer system comprising, e.g., maleic anhydride, and at least one other addition monomer.
U.S. Pat. No. 4,171,273 reacts an ethylene copolymer (M.sub.v =10,000 to 100,000) with maleic anhydride in the presence of a free radical initiator and then with mixtures of C.sub.4 to C.sub.12 n-alcohol and amine such as N-aminopropylmorpholine or dimethylamino propyl amine to form a V.I.-dispersant-pour depressant additive.
U.S. Pat. No. 4,517,104 relates to EP and EPDM viscosity index improver-dispersant additives prepared from EP polymer (M.sub.n =5000 to 500,000), by maleic anhydride grafting and reaction with polyamines.
The following references include disclosures of EP/EPDM polymers of M.sub.n of 700/500,000, also prepared by conventional Ziegler catalysts.
U.S. Pat. No. 4,089,794 teaches grafting the ethylene copolymer (M.sub.n =700 to 500,000) with maleic anhydride using peroxide in a lubricating oil solution, wherein the grafting is preferably carried out under nitrogen, followed by reaction with polyamine.
U.S. Pat. No. 4,137,185 teaches reacting C.sub.1 to C.sub.30 monocarboxylic acid anhydrides, and dicarboxylic anhydrides, such as acetic anhydride, succinic anhydride, etc., with an ethylene copolymer (M.sub.n =700 to 500,000) reacted with maleic anhydride and a polyalkylene polyamine to inhibit cross linking and viscosity increase due to further reaction of any primary amine groups which were initially unreacted.
U.S. Pat. No. 4,144,181 is similar to 4,137,185 in that it teaches using a sulfonic acid to inactivate the remaining primary amine groups when a maleic anhydride grafted ethylene-propylene copolymer (M.sub.n =700 to 500,000) is reacted with a polyamine.
U.S. Pat. No. 4,219,432 teaches maleic anhydride grafted ethylene copolymer (M.sub.n =700 to 500,000) reacted witch a mixture of an amine having only one primary group together with a second amine having two or more primary groups.
Related disclosures of maleic anhydride grafted, aminated ethylene-propylene polymer viscosity improver-dispersant additives useful in lubricating oil compositions are contained in U.S. Pat. Nos. 4,507,515; 4,557,847; 4,632,769; 4,693,838; and 4,707,285.
U.S. Pat. No. 4,668,834 to Uniroyal Chemical discloses preparation (via certain metallocene and alumoxane catalyst systems) and composition of ethylene-alpha olefin copolymers and terpolymers having vinylidene-type terminal unsaturation, which are disclosed to be useful as intermediates in epoxy-grafted encapsulation compositions.
U.S. Pat. No. 4,704,491 to Mitsui Petrochemical relates to liquid ethylene alpha-olefin random copolymers, useful when hydrogenated as synthetic lubricant oil, characterized inter alia by having 10-85 mol. % ethylene units, 15-90 mol. % alpha-olefin units, M.sub.n of from 300 to 10,000 and a M.sub.w /M.sub.n of not more than 2.5. The patent also indicates that the liquid copolymer can be easily modified since it has a double bond capable of reacting with maleic anhydride, etc., at the molecular chain ends.
Japanese Published Patent Application 87-129,303A of Mitsui Petrochemical relates to narrow molecular weight distribution (M.sub.w /M.sub.n &lt;2.5) ethylene alpha-olefin copolymer waxes containing 85-99 mol % ethylene, which are disclosed to be used for dispersing agents, modifiers or materials to produce toners. The copolymers (having crystallinity of from 5-85%) are prepared in the presence of a catalyst system comprising Zr compounds having at least one cycloalkadienyl group and alumoxane.
European Patent 128,046 discloses (co)polyolefin reactor blends of polyethylene and ethylene higher alpha-olefin copolymers prepared by employing described dual-metallocene/alumoxane catalyst systems.
European Patent Publication 129,368 discloses metallocene/alumoxane catalysts useful for the preparation of ethylene homopolymer and ethylene higher alpha-olefin copolymers.
European Patent Application Publication 257,696 A1 relates to a process for dimerizing alpha-olefins using a catalyst comprising certain metallocene/alumoxane systems.
European Patent Publication 305,022-A1 to Mitsui Petrochemical relates to certain synthetic hydrocarbon lubricating oil compositions containing a load-withstanding additive and a liquid ethylene alpha-olefin random copolymer modified by graft copolymerization with an unsaturated carboxylic acid or derivative thereof (e.g., maleic anhydride). The ethylene alpha-olefin copolymers (M.sub.n of 300 to 12,000) are obtained using Ziegler catalysts (e.g., catalyst formed from soluble V compound and an organo aluminum compound), are grafted in the presence of a free radical initiator.
PCT Published Patent Application WO 88/01626 relates to transition metal compound/alumoxane catalysts for polymerizing alpha-olefins.